Re: New Cyanotype - my first unsuccessful attempt

From: "Christina Z. Anderson" <zphoto@bellsouth.net>
Subject: Re: New Cyanotype - my first unsuccessful attempt
Date: Thu, 19 Aug 2004 14:36:59 -0400

> Next question; why, do you think, or any chemists have a clue, would
> citric acid cause fading but not nitric or hydrochloric?

Sorry to make it boring, but this seems to be something that should be
verified for its repeatability first. As far as I saw in this thread,
there was one anecdotal report and we aren't very sure if this is real
and indeed citric acid and light are involved.

A test would be something like this. A piece of cyanotype should be
exposed as evenly as possible (or better expose with 4 step wedges),
process it as evenly as possible, and cut them in 4 pieces. Parts 1
and 2 should be treated in citric acid bath and thoroughly
washed. Parts 3 and 4 are just thoroughly washed. Parts 2 and 4 should
be exposed to intense light while 1 and 3 should be stored in cool,
dark place. If only part 2 loses its density appreciably while others
are unchanged, the test is consistent with the anecdotal report. Then
lack of fading with nitric acid should be tested similarly.

There are dozen possibilities that can be argued but I don't think any
of them is particularly likely.

I routinely form Prussian blue at pH of 7.4. The specimen is stored
and processed at pH 7.4 taking a few days. I keep those specimen in
dark at room temperature, but they get exposed to intense light for
microscopic examination occasionally. I don't read their densities
because individual spots are very small, but I don't see any sign of
fading or disappearing in a year or two. For that matter, people have
used this technique for decades but I've never heard of an old
specimen that went faded.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)